How clean are clean surfaces?

Starting materials

8 sterile cotton swabs
Test tube of sterile water
Masking tape
8 nutrient agar petri plates
Directable flame source (e.g.: plumber's propane torch)
Aluminum foil

Methods

1 You will need 8 nutrient agar plates. Label them from "A" to "H". Click to learn how to make beginner's nutrient agar plates.
Along with sterilizing the stuff for the agar plates, sterilize a test tube half full of water. Cover the tube with aluminum foil prior to sterilizing.
DO NOT CONTINUE until your petri plates are ready to use.
2 Clear off but do not clean a desktop that is made of fire resistant material. And then divide the surface into 8 different areas using masking tape. With a pen, label each area from "A" to "H".
3 Decide on which cleaning agent you will us. Suggestions:

Control (nothing done to sector
Rubbed off with dry cloth
Rubbed off with wet cloth
Rubbed off with ordinary detergent and then water
Rubbed with antibacterial detergent and then water
Rubbed with cloth containing ethanol
Rubbed with cloth containing 1/30 bleach and then water
LIGHTLY flamed using the plumber's torch

4 Each student moistens a swab in the sterile water, wiggles the swab around in the MIDDLE of an assigned sector, and then smears the swab around on the surface of the appropriately lettered agar plate.
5 Set the plates aside. Daily take note of what is seen in each plate. In particular note the presence of each of the following: Types of things seen:
fuzzy molds
small dots (colonies) that are not fuzzy
How many different kinds of each of the above.
The succession:
which kinds grew up first, and then which grew, and so on.
6 CLEAN UP! Do not allow your plates to sit around and stink up the place! To dispose of the putrid, disgusting stuff, dribble a little household bleach directly onto the surfaces of the agar and tilt the plates to get the bleach to cover the whole surface. Instantaneous death to the microbes! Make sure that you splash the bleach onto your skin and clothes. Imagine the increasing pain as the bleach attacks you, and the racing stripes you will get on your clothes!
If you are using disposable plates, drain the excess bleach into a sink with running water, and trash the plates and their disgusting agar. If you are using non-disposable plates, allow the bleach to sit overnight, drain liquid into a sink, and then using a stick or spatula dig the agar out and flip into a trash can. Then wash the plates thoroughly.
7 Now to turn your observations into SCIENCE. There are two ways to slice this "pie:" One is to look at which cleaning technique eliminated the most microbes, and the second way is to look at which technique was able to kill which sorts of microbes. We are, afterall, mainly interested in killing harmful microbes. Thus sit down with your colleagues (in other words the teacher and students). Designate two chalkboards for the two different perspectives, and have a student stand by each board to write down conclusions appropriate to that perspective.
8 Extend your conclusions into new hypotheses (Let Science March On!). Suppose you were doing this experiment not with table tops but with hands. How would you run this new experiment - ah, without swabs, for example? And what findings do you think you will get? Ah, ha! You had better run off and do that to check out your thinking. Nothing works like the "imperical method" - try it and see! (Yes, teacher, you may intersect that last statement with Immanuel Kant and the philosophy of rational impericism upon which our scientific age was founded! (Yeah, sure!))
9 Have you heard the term "probiotics?" It is about using good microbes to fight bad ones. Add this concept into your discussion of the use of antibacterial hand cleaners. Have you considered that many of these good bacteria might be normal residents of your hands (and other parts of your body, too)? Finally, consider that the National Centers for Disease Control and Prevention has been finding a rise in skin infections in the country, and that the rise is due to the use of antibacterial cleaners.
10 Here is a different perspective which you might consider. Door knobs, faucet handles, railing, coins, etc., are touched by many people. Might these surfaces be involved in the spread of disease? Do you think that it might be possible to make these daily items out of materials that are self-sterilizing? How would you test your hypotheses?

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1	You will need 8 nutrient agar plates. Label them from "A" to "H".	Click to learn how to make beginner's nutrient agar plates.
1	Along with sterilizing the stuff for the agar plates, sterilize a test tube half full of water. Cover the tube with aluminum foil prior to sterilizing.
DO NOT CONTINUE until your petri plates are ready to use.
2	Clear off but do not clean a desktop that is made of fire resistant material. And then divide the surface into 8 different areas using masking tape. With a pen, label each area from "A" to "H".
3	Decide on which cleaning agent you will us.	Suggestions: Control (nothing done to sector Rubbed off with dry cloth Rubbed off with wet cloth Rubbed off with ordinary detergent and then water Rubbed with antibacterial detergent and then water Rubbed with cloth containing ethanol Rubbed with cloth containing 1/30 bleach and then water LIGHTLY flamed using the plumber's torch
4	Each student moistens a swab in the sterile water, wiggles the swab around in the MIDDLE of an assigned sector, and then smears the swab around on the surface of the appropriately lettered agar plate.
5	Set the plates aside. Daily take note of what is seen in each plate. In particular note the presence of each of the following:	Types of things seen: fuzzy molds small dots (colonies) that are not fuzzy How many different kinds of each of the above. The succession: which kinds grew up first, and then which grew, and so on.
6	CLEAN UP! Do not allow your plates to sit around and stink up the place! To dispose of the putrid, disgusting stuff, dribble a little household bleach directly onto the surfaces of the agar and tilt the plates to get the bleach to cover the whole surface. Instantaneous death to the microbes! Make sure that you splash the bleach onto your skin and clothes. Imagine the increasing pain as the bleach attacks you, and the racing stripes you will get on your clothes! If you are using disposable plates, drain the excess bleach into a sink with running water, and trash the plates and their disgusting agar. If you are using non-disposable plates, allow the bleach to sit overnight, drain liquid into a sink, and then using a stick or spatula dig the agar out and flip into a trash can. Then wash the plates thoroughly.
7	Now to turn your observations into SCIENCE. There are two ways to slice this "pie:" One is to look at which cleaning technique eliminated the most microbes, and the second way is to look at which technique was able to kill which sorts of microbes. We are, afterall, mainly interested in killing harmful microbes. Thus sit down with your colleagues (in other words the teacher and students). Designate two chalkboards for the two different perspectives, and have a student stand by each board to write down conclusions appropriate to that perspective.
8	Extend your conclusions into new hypotheses (Let Science March On!). Suppose you were doing this experiment not with table tops but with hands. How would you run this new experiment - ah, without swabs, for example? And what findings do you think you will get? Ah, ha! You had better run off and do that to check out your thinking. Nothing works like the "imperical method" - try it and see! (Yes, teacher, you may intersect that last statement with Immanuel Kant and the philosophy of rational impericism upon which our scientific age was founded! (Yeah, sure!))
9	Have you heard the term "probiotics?" It is about using good microbes to fight bad ones. Add this concept into your discussion of the use of antibacterial hand cleaners. Have you considered that many of these good bacteria might be normal residents of your hands (and other parts of your body, too)? Finally, consider that the National Centers for Disease Control and Prevention has been finding a rise in skin infections in the country, and that the rise is due to the use of antibacterial cleaners.
10	Here is a different perspective which you might consider. Door knobs, faucet handles, railing, coins, etc., are touched by many people. Might these surfaces be involved in the spread of disease? Do you think that it might be possible to make these daily items out of materials that are self-sterilizing? How would you test your hypotheses?